Sheet metal is commonly formed utilizing a combination of hot rolling and cold rolling to reduce an initial slab of metal into a coil of sheet having a desired thickness and metallurgical properties. Traditionally, the hot strip rolling and cold rolling operations are done separately. The initial sheet metal forming process begins with a large slab of metal. The slab may be inches thick and weigh several tons. The metal slab is initially heated in an oven to a forming temperature, which is approximately 2000.degree. F. for steel. Once the forming temperature is achieved, the metal slab is horizontally transferred through a series of rollers which sequentially reduce the slab thickness. Frequently, the metal thickness is reduced to approximately 3/8"-3/4" during hot rolling, with the final thickness to be achieved subsequently in a cold rolling operation.
As the metal sheet slab progresses through the series of rollers, the slab initially goes through a roughing mill, and finally through a finishing mill. During the rolling process, the temperature of the sheet typically drops to approximately 1400.degree. to 1750.degree. F. at the mill exit. After the sheet exits the last rolling station, the sheet is cooled using coolant sprays until the temperature is dropped sufficiently to allow the strip to be coiled, i.e., approximately 850.degree. to 1200.degree. F. depending upon material and gage. Water sprays are typically used as a cooling medium In the past, coolant flow has been adjusted based upon an average strip temperature measurement, as shown in U.S. Pat. Nos. 3,613,418, 3,905,216, and 4,274,273, which are incorporated by reference herein. As the metal strip cools, metallurgical characteristics of the sheet are determined. There has been a great emphasis on achieving improved sheet metal quality by controlling the cold rolling operation, while the hot strip rolling process has gone relatively ignored.